Surface-guided tomotherapy improves positioning and reduces treatment time: A retrospective analysis of 16 835 treatment fractions

Setup margins based on the inter- and intrafractional setup error of left-sided breast cancer radiotherapy using deep inspiration breath-hold technique (DIBH) and surface guided radiotherapy (SGRT)

PURPOSE

The use of volumetric modulated arc therapy (VMAT), simultaneous integrated boost (SIB), and hypofractionated regimen requires adequate patient setup accuracy to achieve an optimal outcome. The purpose of this study was to assess the setup accuracy of patients receiving left-sided breast cancer radiotherapy using deep inspiration breath-hold technique (DIBH) and surface guided radiotherapy (SGRT) and to calculate the corresponding setup margins.

METHODS

The patient setup accuracy between and within radiotherapy fractions was measured by comparing the 6DOF shifts made by the SGRT system AlignRT with the shifts made by kV-CBCT. Three hundred and three radiotherapy fractions of 23 left-sided breast cancer patients using DIBH and SGRT were used for the analysis. All patients received pre-treatment DIBH training and visual feedback during DIBH. An analysis of variance (ANOVA) was used to test patient setup differences for statistical significance. The corresponding setup margins were calculated using the van Herk's formula.

RESULTS

The intrafractional patient setup accuracy was significantly better than the interfractional setup accuracy (p < 0.001). The setup margin for the combined inter- and intrafractional setup error was 4, 6, and 4 mm in the lateral, longitudinal, and vertical directions if based on SGRT alone. The intrafractional error contributed ≤1 mm to the calculated setup margins.

CONCLUSION

With SGRT, excellent intrafractional and acceptable interfractional patient setup accuracy can be achieved for the radiotherapy of left-sided breast cancer using DIBH and modern radiation techniques. This allows for reducing the frequency of kV-CBCTs, thereby saving treatment time and radiation exposure.

Surface guided radiotherapy practice in paediatric oncology: a survey on behalf of the SIOPE Radiation Oncology Working Group

INTRODUCTION

Surface guided radiotherapy (SGRT) is increasingly being implemented to track patient's surface movement and position during radiation therapy. However, limited information is available on the SGRT use in paediatrics. The aim of this double survey was to map SIOPE (European Society for Paediatric Oncology)-affiliated centres using SGRT and to gain information on potential indications, observed, or expected benefits.

METHODS

A double online survey was distributed to 246 SIOPE-affiliated radiotherapy (RT) centres. Multiple choices, yes/no, and open answers were included. The first survey (41 questions) was active from February to March 2021. A shortened version (13 questions) was repeated in March 2023 to detect trends in SGRT use within the same community.

RESULTS

Respectively, 76/142 (54%) and 28/142 (20%) responding centres used and planned to use SGRT clinically, including 4/34 (12%) new centres since 2021. Among the SGRT users, 33/76 (43%) already applied this technology to paediatric treatments. The main benefits of improved patient comfort, better monitoring of intrafraction motion, and more accurate initial patient set-up expected by future users did not differ from current SGRT-users (P = .893). Among non-SGRT users, the main hurdles to implement SGRT were costs and time for installation. In paediatrics, SGRT is applied to all anatomical sites.

CONCLUSION

This work provides information on the practice of SGRT in paediatrics across SIOPE-affiliated RT centres which can serve as a basis for departments when considering the purchase of SGRT systems.

ADVANCES IN KNOWLEDGE

Since little information is available in the literature on the use of SGRT in paediatrics, the results of this double survey can serve as a basis for departments treating children when considering the purchase of an SGRT system.

Development and evaluation of a novel water-based pigment marker for radiation therapy skin marking

Skin marks are widely used in external radiation therapy to ensure the accuracy of the irradiation position. However, conventional skin markers contain harmful substance, so we developed an alternative skin marker. The purpose of this study was to investigate the feasibility of using a novel water-based pigment marker comprising safe materials commonly used in cosmetics for clinical radiation therapy. We investigated various properties of the marker, namely marker longevity, color variety, line visibility, ink bleeding, and line durability, and improved the marker in response to the feel when drawing or being drawn on. The durability of the ink was evaluated by simultaneously applying the new marker and oil-based pen and comparing the period until the marks faded and became invisible. In clinical trial, we applied marks on the skin of 56 patients over three months to observe symptoms and visible changes in the skin. There were no complications of discomfort or pain, owing to the improvements in the marker tip. The marks drawn on the arms of volunteers with the new marker and the oil-based pen remained visible for a mean of 7.2 days and 3.6 days, respectively (P value < 0.001). The percentages of participants with no symptoms and no visible changes were 100%, respectively. We developed an alternative skin marker that complies with current regulatory standards by excluding crystal violet. The newly developed marker has features suitable for clinical use, such as resistance to smudging and water, marker tip shape and texture, and color variations.

Considerations for intensity modulated total body or total marrow and lymphoid irradiation

We compiled a sampling of the treatment techniques of intensity-modulated total body irradiation, total marrow irradiation and total marrow and lymphoid irradiation utilized by several centers across North America and Europe. This manuscript does not serve as a consensus guideline, but rather is meant to serve as a convenient reference for centers that are considering starting an intensity-modulated program.

Setup accuracy and margins for surface-guided radiotherapy (SGRT) of head, thorax, abdomen, and pelvic target volumes

The goal of the study was to evaluate the inter- and intrafractional patient setup accuracy of target volumes located in the head, thoracic, abdominal, and pelvic regions when using SGRT, by comparing it with that of laser alignment using patient skin marks, and to calculate the corresponding setup margins. A total of 2303 radiotherapy fractions of 183 patients were analyzed. All patients received daily kilovoltage cone-beam computed tomography scans (kV-CBCT) for online verification. From November 2019 until September 2020, patient setup was performed using laser alignment with patient skin marks, and since October 2020, using SGRT. The setup accuracy was measured by the six degrees of freedom (6DOF) corrections based on the kV-CBCT. The corresponding setup margins were calculated using the van Herk formula. Analysis of variance (ANOVA) was used to evaluate the impact of multiple factors on the setup accuracy. The inter-fractional patient setup accuracy was significantly better using SGRT compared to laser alignment with skin marks. The mean three-dimensional vector of the translational setup deviation of tumors located in the thorax, abdomen, and pelvis using SGRT was 3.6 mm (95% confidence interval (CI) 3.3 mm to 3.9 mm) and 4.5 mm using laser alignment with skin marks (95% CI 3.9 mm to 5.2 mm; p = 0.001). Calculation of setup margins for the combined inter- and intra-fractional setup error revealed similar setup margins using SGRT and kV-CBCT once a week compared to laser alignment with skin marks and kV-CBCT every other day. Furthermore, comparable setup margins were found for open-face thermoplastic masks with AlignRT compared to closed-face thermoplastic masks with laser alignment and mask marks. SGRT opens the possibility to reduce the number of CBCTs while maintaining sufficient setup accuracy. The advantage is a reduction of imaging dose and overall treatment time. Open-face thermoplastic masks may be used instead of closed-face thermoplastic masks to increase the patient's comfort.

Application of surface-guided radiation therapy in prostate cancer: comparative analysis of differences with skin marking-guided patient setup

PURPOSE

Surface-guided radiation therapy is an image-guided method using optical surface imaging that has recently been adopted for patient setup and motion monitoring during treatment. We aimed to determine whether the surface guide setup is accurate and efficient compared to the skin-marking guide in prostate cancer treatment.

MATERIALS AND METHODS

The skin-marking setup was performed, and vertical, longitudinal, and lateral couch values (labeled as "M") were recorded. Subsequently, the surface-guided setup was conducted, and couch values (labeled as "S") were recorded. After performing cone-beam computed tomography (CBCT), the final couch values was recorded (labeled as "C"), and the shift value was calculated (labeled as "Gap (M-S)," "Gap (M-C)," "Gap (S-C)") and then compared. Additionally, the setup times for the skin marking and surface guides were also compared.

RESULTS

One hundred and twenty-five patients were analyzed, totaling 2,735 treatment fractions. Gap (M-S) showed minimal differences in the vertical, longitudinal, and lateral averages (-0.03 cm, 0.07 cm, and 0.06 cm, respectively). Gap (M-C) and Gap (S-C) exhibited a mean difference of 0.04 cm (p = 0.03) in the vertical direction, a mean difference of 0.35 cm (p = 0.52) in the longitudinal direction, and a mean difference of 0.11 cm (p = 0.91) in the lateral direction. There was no correlation between shift values and patient characteristics. The average setup time of the skin-marking guide was 6.72 minutes, and 7.53 minutes for the surface guide.

CONCLUSION

There was no statistically significant difference between the surface and skin-marking guides regarding final CBCT shift values and no correlation between translational shift values and patient characteristics. We also observed minimal difference in setup time between the two methods. Therefore, the surface guide can be considered an accurate and time-efficient alternative to skin-marking guides.

Development of a new coordinate calibration phantom for a light-section-based optical surface monitoring system

A calibration phantom made of Derlin requires manual translational and rotational adjustments when calibrating a light-section-based optical surface monitoring system (VOXELAN) with a phantom material that insufficiently reflects the red-slit laser of the system. This study aimed to develop a new calibration phantom using different materials and to propose a procedure that minimizes setup errors. The new phantom, primarily made of PET100, which exhibits good reflectivity without scattering or attenuating the red-slit laser at the phantom surface, was shaped in a manner similar to that of previous designs. The detection accuracy and stability were evaluated using six different regions of interest (ROIs) and compared with previous phantom designs. The coordinate coincidence between the machine and VOXELAN was compared for both phantom designs. The detection accuracy and stability of the new phantom in the reference ROI setting were found to be better than those of previous phantoms. In the lateral, longitudinal, and vertical directions, the coordinate coincidences in translational directions for the previous phantom were obtained at 1.07 ± 0.66, 1.46 ± 0.47, and 0.26 ± 0.83 mm, whereas those for the new phantom were obtained at 0.28 ± 0.21, 0.18 ± 0.30, and - 0.30 ± 0.29 mm, respectively. The rotational errors of the two phantoms were identical. The new phantom exhibited improved detection stability because of its good reflectivity. Additionally, the new placement procedure was linked to the six-degrees-of-freedom couch. A combination of the new phantom and its new placement procedure is suitable for coordinate calibration of VOXELAN.

Surface guided electron FLASH radiotherapy for canine cancer patients

BACKGROUND

During recent years FLASH radiotherapy (FLASH-RT) has shown promising results in radiation oncology, with the potential to spare normal tissue while maintaining the antitumor effects. The high speed of the FLASH-RT delivery increases the need for fast and precise motion monitoring to avoid underdosing the target. Surface guided radiotherapy (SGRT) uses surface imaging (SI) to render a 3D surface of the patient. SI provides real-time motion monitoring and has a large scanning field of view, covering off-isocentric positions. However, SI has so far only been used for human patients with conventional setup and treatment.

PURPOSE

The aim of this study was to investigate the performance of SI as a motion management tool during electron FLASH-RT of canine cancer patients.

METHODS

To evaluate the SI system's ability to render surfaces of fur, three fur-like blankets in white, grey, and black were used to imitate the surface of canine patients and the camera settings were optimized for each blanket. Phantom measurements using the fur blankets were carried out, simulating respiratory motion and sudden shift. Respiratory motion was simulated using the QUASAR Respiratory Motion Phantom with the fur blankets placed on the phantom platform, which moved 10 mm vertically with a simulated respiratory period of 4 s. Sudden motion was simulated with an in-house developed phantom, consisting of a platform which was moved vertically in a stepwise motion at a chosen frequency. For sudden measurements, 1, 2, 3, 4, 5, 6, 7, and 10 Hz were measured. All measurements were both carried out at the conventional source-to-surface distance (SSD) of 100 cm, and in the locally used FLASH-RT setup at SSD = 70 cm. The capability of the SI system to reproduce the simulated motion and the sampling time were evaluated. As an initial step towards clinical implementation, the feasibility of SI for surface guided FLASH-RT was evaluated for 11 canine cancer patients.

RESULTS

The SI camera was capable of rendering surfaces for all blankets. The deviation between simulated and measured mean peak-to-peak breathing amplitude was within 0.6 mm for all blankets. The sampling time was generally higher for the black fur than for the white and grey fur, for the measurement of both respiratory and sudden motion. The SI system could measure sudden motion within 62.5 ms and detect motion with a frequency of 10 Hz. The feasibility study of the canine patients showed that the SI system could be an important tool to ensure patient safety. By using this system we could ensure and document that 10 out of 11 canine patients had a total vector offset from the reference setup position <2 mm immediately before and after irradiation.

CONCLUSIONS

We have shown that SI can be used for surface guided FLASH-RT of canine patients. The SI system is currently not fast enough to interrupt a FLASH-RT beam while irradiating but with the short sampling time sudden motion can be detected. The beam can therefore be held just prior to irradiation, preventing treatment errors such as underdosing the target.

Verification of patient‐setup accuracy using a surface imaging system with steep measurement angle

PURPOSE

We evaluate an SGRT device (Voxelan HEV-600 M/RMS) installed with Radixact, with the view angle of the Voxelan's camera at 74 degrees. The accuracy of Voxelan with this steep angle was evaluated with phantom experiments and inter-fractional setup errors of patients.

METHODS

In the phantom experiments, the difference between the measured values of Voxelan from the truth was evaluated for translations and rotations. The inter-fractional setup error between the setup using skin markers with laser localizer (laser setup: LS) and the setup using Voxelan (surface setup: SS) was compared for head and neck (N = 19), chest (N = 7) and pelvis (N = 9) cases. The inter-fractional setup error was calculated by subtracting from bone matching by megavoltage computed tomography (MVCT) as ground truth.

RESULTS

From the phantom experiments, the average difference between the measured values of Voxelan from the truth was within 1 mm and 1 degree. In all cases, inter-fractional setup error based on MVCT was not significantly different between LS and SS by Welch's t-test (P > 0.05). The vector offset of the LS for head and neck, chest, and pelvis were 6.5, 9.6, and 9.6 mm, respectively, and that of the SS were 5.8, 8.6, and 12.6 mm, respectively. Slight improvement was observed for the head and neck, and chest cases, however, pelvis cases were not improved because the umbilical region could not be clearly visualized as a reference.

CONCLUSION

The results show that SS in Voxelan with an installation angle of 74 degrees is equal to or better than LS.

Advances and potential of optical surface imaging in radiotherapy

This article reviews the recent advancements and future potential of optical surface imaging (OSI) in clinical applications as a four-dimensional (4D) imaging modality for surface-guided radiotherapy (SGRT), including OSI systems, clinical SGRT applications, and OSI-based clinical research. The OSI is a non-ionizing radiation imaging modality, offering real-time 3D surface imaging with a large field of view (FOV), suitable for in-room interactive patient setup, and real-time motion monitoring at any couch rotation during radiotherapy. So far, most clinical SGRT applications have focused on treating superficial breast cancer or deep-seated brain cancer in rigid anatomy, because the skin surface can serve as tumor surrogates in these two clinical scenarios, and the procedures for breast treatments in free-breathing (FB) or at deep-inspiration breath-hold (DIBH), and for cranial stereotactic radiosurgery (SRS) and radiotherapy (SRT) are well developed. When using the skin surface as a body-position surrogate, SGRT promises to replace the traditional tattoo/laser-based setup. However, this requires new SGRT procedures for all anatomical sites and new workflows from treatment simulation to delivery. SGRT studies in other anatomical sites have shown slightly higher accuracy and better performance than a tattoo/laser-based setup. In addition, radiographical image-guided radiotherapy (IGRT) is still necessary, especially for stereotactic body radiotherapy (SBRT). To go beyond the external body surface and infer an internal tumor motion, recent studies have shown the clinical potential of OSI-based spirometry to measure dynamic tidal volume as a tumor motion surrogate, and Cherenkov surface imaging to guide and assess treatment delivery. As OSI provides complete datasets of body position, deformation, and motion, it offers an opportunity to replace fiducial-based optical tracking systems. After all, SGRT has great potential for further clinical applications. In this review, OSI technology, applications, and potential are discussed since its first introduction to radiotherapy in 2005, including technical characterization, different commercial systems, and major clinical applications, including conventional SGRT on top of tattoo/laser-based alignment and new SGRT techniques attempting to replace tattoo/laser-based setup. The clinical research for OSI-based tumor tracking is reviewed, including OSI-based spirometry and OSI-guided tumor tracking models. Ongoing clinical research has created more SGRT opportunities for clinical applications beyond the current scope.

Surface guided radiation therapy: An international survey on current clinical practice

Introduction

Surface Guided Radiation Therapy (SGRT) is being increasingly implemented into clinical practice across a number of techniques and irradiation-sites. This technology, which is provided by different vendors, can be used with most simulation- and delivery-systems. However, limited guidelines and the complexity of clinical settings have led to diverse patterns of operation. With the aim to understand current clinical practice a survey was designed focusing on specifics of the clinical implementation and usage.

Materials and methods

A 32-question survey covered: type and number of systems, quality assurance (QA), clinical workflows, and identification of strengths/limitations. Respondents from different professional groups and countries were invited to participate. The survey was distributed internationally via ESTRO-membership, social media and vendors.

Results

Of the 278 institutions responding, 172 had at least one SGRT-system and 136 use SGRT clinically. Implementation and QA were primarily based on the vendors' recommendations and phantoms. SGRT was mainly implemented in breast RT (116/136), with strong but diverse representation of other sites. Many (58/135) reported at least partial elimination of skin-marks and a third (43/126) used open-masks. The most common imaging protocol reported included the combination of radiographic imaging with SGRT. Patient positioning (115/136), motion management (104/136) and DIBH (99/136) were the main applications.Main barriers to broader application were cost, system integration issues and lack of demonstrated clinical value. A lack of guidelines in terms of QA of the system was highlighted.

Conclusions

This overview of the SGRT status has the potential to support users, vendors and organisations in the development of practices, products and guidelines.

Feasibility of surface guided radiotherapy for patient positioning in breast radiotherapy versus conventional tattoo-based setups- a systematic review

Background

Traditionally tattoos are used for patient setup in radiotherapy. However they may pose challenges for the radiotherapists to achieve precise patient alignment, and serve as a permanent visual reminder of the patient’s diagnosis and often challenging cancer journey. The psychological impact of tattoos has been recognized in recent years. The increasing complexity of treatment techniques and the utilization of hypofractionated regimes, requires an enhanced level of accuracy and safety. Surface guided radiotherapy (SGRT) enables improvements in the accuracy and reproducibility of patient isocentric and postural alignment, enhanced efficiency, and safety in breast radiotherapy.

Purpose

The aim of this review was to compare the accuracy and reproducibility of SGRT to conventional tattoo-based setups in free-breathing breast radiotherapy and to determine if SGRT can reduce the frequency of routine image guided radiotherapy (IGRT).

Materials and Methods

A systematic literature review was performed as per PRISMA guidelines. Papers identified through PubMed, Embase, Web of Science and Google Scholar database searches between 2010 and 2021, were critically appraised. Systematic, random, mean residual errors and 3D vector shifts as determined by IGRT verification were analysed.

Results

A review of 13 full papers suggests SGRT improves the accuracy and reproducibility of patient setup in breast radiotherapy with consistent reductions in the residual errors. There appears to be a good correlation between SGRT setups and radiographic imaging. The frequency of IGRT and the corresponding dose could potentially be reduced. Additionally, SGRT improves treatment efficiency.

Conclusion

SGRT appears to have improved the accuracy and reproducibility of patient setup and treatment efficiency of breast radiotherapy compared to conventional tattoo/laser-based method, with the potential to reduce the frequency of routine IGRT. The reliance on tattoos in breast radiotherapy are likely to become obsolete with positive implications for both patients and clinical practice.

ESTRO-ACROP guideline on surface guided radiation therapy

Surface guidance systems enable patient positioning and motion monitoring without using ionising radiation. Surface Guided Radiation Therapy (SGRT) has therefore been widely adopted in radiation therapy in recent years, but guidelines on workflows and specific quality assurance (QA) are lacking. This ESTRO-ACROP guideline aims to give recommendations concerning SGRT roles and responsibilities and highlights common challenges and potential errors. Comprehensive guidelines for procurement, acceptance, commissioning, and QA of SGRT systems installed on computed tomography (CT) simulators, C-arm linacs, closed-bore linacs, and particle therapy treatment systems are presented that will help move to a consensus among SGRT users and facilitate a safe and efficient implementation and clinical application of SGRT.

Surface-guided radiotherapy for lung cancer can reduce the number of close patient contacts without compromising initial setup accuracy

Surface-guided radiotherapy (SGRT) can assist with patient setup by providing a real-time feedback mechanism over the whole patient treatment surface. It also has the potential to reduce the number of close contacts between staff and the patient, which is advocated for infection control during the COVID-19 pandemic. Residual translations and rotations (post-CBCT) were acquired following a conventional setup protocol (using permanent marks and lasers) and an SGRT setup protocol. The SGRT protocol resulted in one of the two therapeutic radiographers not having any close contact (<2m) with a patient during setup. Data from 702 imaging sessions showed similar setup accuracy with either protocol, fewer large translations and fewer repeat setup occurrences using the SGRT protocol. The potential of SGRT for infection control should be recognised alongside other benefits.

Faster and more accurate patient positioning with surface guided radiotherapy for ultra-hypofractionated prostate cancer patients

INTRODUCTION

The aim of this study was to evaluate if surface guided radiotherapy (SGRT) can decrease patient positioning time for localized prostate cancer patients compared to the conventional 3-point localization setup method. The patient setup accuracy was also compared between the two setup methods.

MATERIALS AND METHODS

A total of 40 localized prostate cancer patients were enrolled in this study, where 20 patients were positioned with surface imaging (SI) and 20 patients were positioned with 3-point localization. The setup time was obtained from the system log files of the linear accelerator and compared between the two methods. The patient setup was verified with daily orthogonal kV images which were matched based on the implanted gold fiducial markers. Resulting setup deviations between planned and online positions were compared between SI and 3-point localization.

RESULTS

Median setup time was 2:50 min and 3:28 min for SI and 3-point localization, respectively (p < 0.001). The median vector offset was 4.7 mm (range: 0-10.4 mm) for SI and 5.2 mm for 3-point localization (range: 0.41-17.3 mm) (p = 0.01). Median setup deviation in the individual translations for SI and 3-point localization respectively was: 1.1 mm and 1.9 mm in lateral direction (p = 0.02), 1.8 and 1.6 mm in the longitudinal direction (p = 0.41) and 2.2 mm and 2.6 mm in the vertical direction (p = 0.04).

CONCLUSIONS

Using SGRT for positioning of prostate cancer patients provided a faster and more accurate patient positioning compared to the conventional 3-point localization setup.

The role of surface-guided radiation therapy for improving patient safety

Emerging data indicates SGRT could improve safety and quality by preventing errors in its capacity as an independent system in the treatment room. The aim of this work is to investigate the utility of SGRT in the context of safety and quality. Three incident learning systems (ILS) were reviewed to categorize and quantify errors that could have been prevented with SGRT: SAFRON (International Atomic Energy Agency), UW-ILS (University of Washington) and AvIC (Skåne University Hospital). A total of 849/9737 events occurred during the pre-treatment review/verification and treatment stages. Of these, 179 (21%) events were predicted to have been preventable with SGRT. The most common preventable events were wrong isocentre (43%) and incorrect accessories (34%), which appeared at comparable rates among SAFRON and UW-ILS. The proportion of events due to wrong accessories was much smaller in the AvIC ILS, which may be attributable to the mandatory use of SGRT in Sweden. Several case scenarios are presented to demonstrate that SGRT operates as a valuable complement to other quality-improvement tools routinely used in radiotherapy. Cases are noted in which SGRT itself caused incidents. These were mostly related to workflow issues and were of low severity. Severity data indicated that events with the potential to be mitigated by SGRT were of higher severity for all categories except wrong accessories. Improved vendor integration of SGRT systems within the overall workflow could further enhance its clinical utility. SGRT is a valuable tool with the potential to increase patient safety and treatment quality in radiotherapy.

Clinical paradigms and challenges in surface guided radiation therapy: Where do we go from here?

Surface guided radiotherapy (SGRT) is becoming a routine tool for patient positioning for specific clinical sites in many clinics. However, it has not yet gained its full potential in terms of widespread adoption. This vision paper first examines some of the difficulties in transitioning to SGRT before exploring the current and future role of SGRT alongside and in concert with other imaging techniques. Finally, future horizons and innovative ideas that may shape and impact the direction of SGRT going forward are reviewed.